Mechanical durability of reinforced sulfo-phenylated polyphenylene-based proton exchange membranes: Impacts of ion exchange capacity and reinforcement thickness
Seyed Hesam Mirfarsi, Aniket Kumar, Jisung Jeong, Ethan Allan Brown, Michael Adamski, Scot Jones, Scott McDermid, Benjamin Britton, Erik Kjeang
Abstract
This work explores the impacts of ion exchange capacity (IEC) and reinforcement thickness on the mechanical durability of reinforced sulfo-phenylated poly(phenylene)-based Pemion® fuel cell membranes . Pressure differential accelerated mechanical stress testing (XP-AMST) is leveraged to rapidly investigate the mechanical durability of reinforced Pemion® and a reference reinforced perfluorosulfonic acid (r-PFSA) ionomer membrane. The fatigue lifetime curves obtained from XP-AMST are explained by in-situ fuel cell performance diagnostics and ex-situ tensile, hygral expansion, stress of dehydration, and crack propagation rate measurements. The rigid-rod poly(phenylene) backbone in Pemion® membranes yields a high stress of dehydration during the dehydration phase, yet superior mechanical fatigue strength in XP-AMST compared to r-PFSA. The XP-AMST results show that reducing the IEC in Pemion® by only 0.3 mmol g −1 can afford three times longer mechanical durability, ∼20 % lower stress of dehydration and hygral swelling, and higher flexibility and dimensional stability in the dry and wet phases, respectively. Furthermore, 2 μm thicker reinforcement yields tougher membranes with suppressed swelling, dehydration stress, and crack propagation rate, improving fatigue longevity. Herein, the importance of tuned IEC and membrane design in the mechanical durability of hydrocarbon-based membranes is highlighted for a viable replacement of incumbent PFSA materials in fuel cells.